A computer, router or switch with the capability to act as a DHCP Server can issue IP addresses dynamically from a range or "pool" of addresses programmed into it. The server responds to a DHCP Request from a DHCP Client with an IP address which it "Leases" to the client for a lease time. Lease time is a parameter set in the DHCP Server that controls when the client must reapply for an IP Address. Some time before the DHCP Lease is scheduled to expire the DHCP Client must renew the lease with the server by sending another DHCP Request. When equipment is removed from a network its IP address will be made available to another network device after the existing lease time expires.